1. Field of the Invention
The present invention relates to an ultrasonic flow meter that measures the flow volume of a liquid flowing through a pipe using ultrasonic waves.
2. Description of the Related Art
An ultrasonic flow meter is known in the prior art that uses ultrasonic waves to function as a flow meter that measures the flow volume of a liquid flowing through a pipe.
This ultrasonic flow meter provides two measuring units having a transducer and provided at an interval in the lengthwise direction on a measuring pipe through which liquid flows. Ultrasonic waves are emitted from one of the transducers which are then received by the other transducer. Alternatively, ultrasonic waves are emitted from the other transducer and then received by the first transducer. The flow rate of the liquid in the measuring pipe is determined from the difference in propagation times of these ultrasonic waves, and flow volume is then measured from this flow rate.
However, although this ultrasonic flow meter has the transducer formed into the shape of a ring and fixed to the measuring pipe inserted into the transducer by adhesive, or has the transducer formed into the shape of a circular arc fixed to the outer periphery of the measuring pipe by adhesive, in these types of structures, there is a risk of variation occurring in the thickness of the adhesive layer in the gap between the transducer and measuring pipe, and in such case, the characteristics of the measurement data fluctuate which causes problems in accurate measurement of flow volume.
Moreover, in a case of such a structure in which the transducer is adhered to the measuring pipe by adhesive, there is the risk of formation of a void composed of air bubbles and so forth of the adhesive between the transducer and pipe, thereby preventing adequate transmission of ultrasonic waves between the transducer and liquid in the pipe, which again has the risk of causing problems in accurate measurement of flow volume.
In consideration of the above circumstances, an object of the present invention is to provide an ultrasonic flow meter that is capable of accurately measuring flow volume.
In order to achieve the above object, the present invention provides an ultrasonic flow meter comprising: a measuring pipe through which liquid flows and two measuring units provided on the measuring pipe at an interval in its lengthwise direction, and which measures flow volume by measuring the flow rate of a liquid from the difference in propagation times of ultrasonic waves in both directions between these measuring units; wherein, each measuring unit has a tubular tightly adhered tube of a prescribed thickness made of material having elasticity attached in the state in which it is tightly adhered to the outer peripheral surface of the measuring pipe, and a transducer maintained in the state in which it is pressed against the outer peripheral surface of the tightly adhered tube.
In other words, since the transducer is attached to the tubular tightly adhered tube of a prescribed thickness made of a material having elasticity, which is attached in a tightly adhered state to the outer periphery of the measuring pipe, in a state in which it is pressed against the tightly adhered tube, the transmission of vibrations between the transducer and fluid inside the measuring pipe can be carried out uniformly, and as a result, the occurrence of fluctuations in measurement data, caused by the transducer being fixed unevenly due to variations in thickness of the adhesive or by air bubbles remaining in the adhesive as in the case of attaching the probe to the measuring pipe with adhesive as in the prior art, can be reliably prevented.
In addition, even in the case of, for example, using adhesive and so forth for fixing a tightly adhered tube, the transducer can be fixed to the measuring pipe with a thin layer and small amount of adhesive. This means that variations in thickness associated with the use of adhesive as well as fluctuations in measurement data caused by residual air bubbles and so forth are prevented. In addition, since ultrasonic waves are transmitted to the transducer or emitted from the transducer through a tightly adhered tube, the ultrasonic waves are maintained in a stable state, or in other words, the sensitivity of the transducer is maintained in a suitable state.
In the ultrasonic flow meter of the present invention, it is preferable that the tightly adhered tube is formed so that its inner diameter is smaller than the outer diameter of the measuring pipe.
Namely, since the inner diameter of the tightly adhered tube is formed to be smaller than the outer diameter of the measuring pipe, by spreading open the tightly adhered tube and attaching to the measuring pipe, the inner peripheral surface of the tightly adhered tube can reliably be suitably tightly adhered to the outer peripheral surface of the measuring pipe.
In this manner, since the tightly adhered tube is fixed to the measuring pipe by fastening the tightly adhered tube itself, there is no need to use an adhesive, and even in the case adhesive is used, adhesive can be provided between the tightly adhered tube and measuring pipe in the form of a thin layer of uniform thickness and without the presence of residual air bubbles.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that an attachment indentation is formed in the measuring pipe over the peripheral direction, and the tightly adhered tube fits into the attachment indentation.
In this manner, by fitting the tightly adhered tube into attachment indentation formed in the measuring pipe, the tightly adhered tube can be reliably attached to a prescribed position of the measuring pipe in which the transducer is fixed.
Furthermore, the measuring units provided along the lengthwise direction of the measuring pipe are required to be arranged at a prescribed interval in terms of measuring flow volume. Therefore, the interval of the measuring units can be reliably determined by specifying the interval of the attachment indentations. In addition, in the case of producing a plurality of ultrasonic flow meters, the interval between the measuring units is maintained constant, thereby resulting in stable product accuracy. In addition, since the position at which the tightly adhered tube fits is specified, assembly work is carried out easily.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that an engaging indentation is formed in the measuring pipe over the peripheral direction, and an engaging protrusion is formed on the inner periphery of the tightly adhered tube over the peripheral direction that engages with the engaging indentation, the tightly adhered tube being attached to the measuring pipe by engaging the engaging indentation and the engaging protrusion.
In this manner, by fitting an engaging protrusion formed on the tightly adhered tube into the engaging indentation formed in the measuring pipe, the tightly adhered tube can be reliably attached to a prescribed position of the measuring pipe in which the transducer is fixed.
Here, it is not necessary to fit the entire tightly adhered tube to the measuring pipe. Furthermore, the shape of the engaging indentation formed in the measuring pipe can be changed as desired to match the shape of the engaging protrusion, or the width of the engaging indentation can be formed to be narrower. Making the width of the engaging indentation narrower results in a reduction in the number of positions where the wall thickness of the measuring pipe is decreased, thereby avoiding a decrease in the strength of the measuring pipe.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that an engaging protrusion is formed on the measuring pipe over the peripheral direction, and an engaging indentation is formed in the inner periphery of the tightly adhered tube over the peripheral direction that is engaged with the engaging protrusion, the tightly adhered tube being attached to the measuring pipe by engaging the engaging protrusion and the engaging indentation.
In this manner, by fitting the engaging indentation formed in the tightly adhered tube into the engaging protrusion formed on the measuring pipe, the tightly adhered tube can be reliably attached to a prescribed position of the measuring pipe in which the transducer is fixed.
In addition, it is not necessary to fit the entire tightly adhered tube. Furthermore, the shape of the engaging protrusion formed on the measuring pipe can be changed as desired to match the shape of the engaging indentation. By providing the engaging protrusion on the measuring pipe, the wall thickness of the measuring pipe is maintained, thereby making it possible to maintain the strength of the measuring pipe.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that the transducer is formed in the shape of a circular arc.
In this manner, by pressing a transducer in the shape of a circular arc onto the outer peripheral surface of a measuring pipe over a tightly adhered tube, the transducer can be evenly attached to the measuring pipe without difficulty.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that the transducer is formed in the shape of a ring.
In this manner, by installing the transducer in the shape of a ring on the outer peripheral surface of a measuring pipe over a tightly adhered tube, the transducer can be evenly attached to the measuring pipe without difficulty.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that a retaining tube is covered over the outer periphery of the measuring unit that tightly adheres the transducer by pressing against the tightly adhered tube.
In this manner, since the transducer is pressed against the tightly adhered tube by the retaining tube, the transducer can be evenly attached to the measuring pipe as a result of being pressed against the measuring pipe. In addition, this retaining tube protecting the transducer having precise structures from external shock. As a result, the durability and reliability of the ultrasonic flow meter can be improved.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that a stepped portion for fitting the above transducer is formed on the tightly adhered tube.
In this manner, the transducer is held in a state in which it is tightly adhered at a prescribed position and without shifting on the outer peripheral surface of the tightly adhered tube. Therefore, the shifting of the transducer is eliminated and accurate measurement of the flow volume can be performed.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that protruding walls that surround the transducer and lie between the transducer and the outside are formed on both sides of the tightly adhered tube, and the transducer is attached between the protruding walls.
In this manner, the transducer is partially separated from the outside by the protruding walls, and together with the attachment position of the transducer being clearly indicated, the transducer is protected from external interference. Therefore, it is possible to improve the durability and reliability of the ultrasonic flow meter. Moreover, in the case the interval between these protruding walls is made to be the width of the transducer, shifting of the transducer can be reliably eliminated, thereby enabling accurate measurement of flow volume.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that a transducer locking member that presses the transducer against the measuring pipe is attached to the protruding walls.
In this manner, the transducer is pressed towards the measuring pipe side from the back surface by the transducer locking member attached to the tightly adhered tube. Therefore, the transducer can be reliably tightly adhered to a tightly adhered tube, thereby enabling accurate measurement of flow volume. In addition, the transducer can be attached without applying a substance such as an adhesive to the contact surface with the tightly adhered tube.
It is further preferable that the transducer locking member is formed equipped with a contacting portion that makes point or linear contact with the back surface of the transducer.
In this manner, differing from that in which the entire back surface is pressed, the transducer is pressed at a partial contacting portion that makes point or linear contact. As a result of the partial position of the back surface of the transducer is pressed, a pressing force is transmitted throughout the entire transducer and deflection of the transducer is obtained thereby resulting in it being reliably tightly adhered to the tightly adhered tube. Therefore, inclination of the transducer and uneven pressing force are eliminated, thereby making it possible to improve the sensitivity of the transducer and accurately measure flow volume. In addition, even in the case of, for example, applying a substance such as an adhesive between the tightly adhered tube and the transducer, the adhesive film can be obtained having a uniform thickness, thereby enabling accurate measurement of flow volume.
Moreover, since the partial position of the transducer at which pressing force is not applied becomes a free end and is not restrained, vibrations of the transducer are reliably obtained resulting in enhanced sensitivity.
Furthermore, in the ultrasonic flow meter of the present invention, it is preferable that a notch or through hole for suspending a lead wire connected to the above transducer is formed in the wall surface of the protruding walls.
In this manner, as a result of the lead wire connected to the transducer is suspended the notch or through hole provided in the wall surface of a protruding wall, excess space required for wiring the lead wire is eliminated, thereby making it possible to realize conservation of space in the vicinity of the measuring unit. In addition, the lead wires can be protected from external interference. Moreover, as a result of suspending the lead wire in the notch or through hole, the transducer is temporarily restrained and the fixed position of the transducer can be determined, thereby making it possible to perform the assembly work of the ultrasonic flow meter easily. In other words, this functions as an auxiliary means of fixing the transducer.